The following are my opions/experiecnce with similar ARs. Your mileage my vary:
1. Is it really worth following any kind of break-in procedure with this chrome-lined bbl? No.
2. I cleaned it and oiled it a bit but didn't do a deep clean... should I bother before I shoot it? I clean all new firearms well prior to shooting. An AR is pretty easy to break down for cleaning. At least clean the barrel, clean and lubricate the bolt carrier group, and clean the inside of the upper reciever. A good wiping out and light oiling of the fire control group in the lower receiver should be sufficient.
3. Any accurizing tips to the bone stock M400? The AR platform is inherently pretty accurate. I'd shoot it first before doing anything. Get a good sling.
4. Deer hunting okay? In my opinion, .223/5.56mm is insufficient for deer hunting (especially when it comes to providing a good blood trail), and there are better calibers available in the AR platform for this. I'm sure there are many who will disagree. Check your local laws regarding the legality of this round for hunting.